March 2, 2000

A weekly feature provided by scientists at the Hawaiian Volcano
Observatory.

The 1955 eruption: spur to a new era of understanding Kilauea

The 1955 eruption in lower Puna, described in last week's column,
was destructive. About 1,580 hectares (3,900 acres) were covered by 108
million cubic meters (141 million cubic yards) of lava, mostly `a`a. Of
the covered land, about 450 hectares (1,100 acres) were under cultivation
in the Kama`ili, Kehena, Ke`eke`e, Kau`eleau, and Kapoho areas.
Approximately 10.1 km (6.3 miles) of public road were buried, as were many
kilometers (miles) of cane-field roads.

Iwasaki Camp, in Kama`ili near the upper big bend in the road to
`Opihikao, was overrun, but fortunately some of the houses and all personal
belongings had been removed. Tragically, surviving remnants of the camp
were destroyed on the last day of the eruption, May 26. In all, 21 houses
were overrun by `a`a during the eruption.

In March, an earthen barrier 300 m (1,000 feet) long and 3 m (10
feet) high was hurriedly bulldozed in an attempt to save Iwasaki Camp.
Twice the flow stopped just after encountering the barrier. But in May,
`a`a followed a different route down the steep slope far from the barrier
and engulfed the camp.

Other barriers were started on March 22 to protect the Yamada
coffee plantation near the coast below Iwasaki Camp. These barriers worked
to some degree, certainly delaying `a`a from penetrating the plantation.
However, part of the Ke`eke`e flow eventually passed beyond the southwest
end of the barriers, and, on March 28, swept across the plantation and into
the sea.

The partial success but ultimate inadequacy of these barriers, and
of those built during the 1960 Kapoho eruption, fuel a controversy that
continues to this day among volcanologists. Feelings run high whenever the
feasibility of lava barriers is discussed. This disagreement is apart from
the social ramifications of diverting lava from one property to another.

A less controversial discovery during the 1955 eruption was that
the summit of Kilauea responded to what was happening in lower
Puna--although only after a delay of about eight days following the start
of the eruption. Before 1955, HVO scientists had speculated that sinking
of the summit area might accompany migration of magma into the east rift
zone. But it was hard to be sure, because the last east-rift eruption
occurred in 1923, when monitoring instruments were both sparse and crude.

In 1955, the rift zone actually swelled near the site of the
initial outbreak on February 28 near Pu`u Honua`ula. The swelling was
detected by the pendulum on a seismograph in Pahoa. Geochemical studies
suggest that the swelling was caused by magma rising from an independent
reservoir in the area, not by pressure from Kilauea's summit. The swelling
was erased by the eruption; repeat surveys made before (for a new highway
southwest of Kapoho) and after the eruption showed sinking and spreading of
several tens of centimeters (more than 1 foot) in the eruptive area.

On March 7, Kilauea's summit began to sink as magma migrated into
the east rift zone to replenish that already erupted. This magma mixed
with some stored in the rift zone and erupted when the vents shifted uprift
of the Pu`u Kali`u area on March 12. Classic geochemical and mineralogic
studies of this magma have led to interpretations that enhance
understanding of the magma plumbing system at Kilauea. Unfortunately, the
magnitude of subsidence accompanying the migration of magma was uncertain
owing to the inadequate instruments of the time.

The 1955 eruption spurred HVO to upgrade its instruments.
Opportunities had been missed for characterizing the ground movements.
Working feverishly during the next 4 1/2 years, Jerry Eaton and colleagues
devised a tiltmeter system and better seismic coverage that were completed
just in time for the 1959 summit and 1960 Kapoho eruptions. The new
instruments provided data about those two eruptions that form the
underpinnings for many of today's ideas about how Hawaiian volcanoes work.

Eruption Update

Eruptive activity of Kilauea Volcano continued unabated during the
past week, and a glow from Pu`u `O`o crater was visible at various times.
Lava is erupting from Pu`u `O`o and flowing through a network of tubes
toward the coast. One flow is entering the ocean at Lae`apuki, and a
second flow, located to the east of the first flow, is active in the area
mauka of Waha`ula. An `a`a flow is cascading down Pulama pali from a
breakout of this eastern flow. The public is reminded that the ocean-entry
areas are extremely hazardous, with explosions accompanying unpredictable
collapses of the new land. The active lava flows are hot and have places
with very thin crust. The steam clouds are highly acidic and laced with
glass particles.

There were no earthquakes reported felt during the week ending on
March 2.

The URL of this page is
http://hvo.wr.usgs.gov/volcanowatch/archive/2000/00_03_02.html
Contact:
hvowebmaster@usgs.govUpdated: 28 Feb 2000